This is what the GIRM (not canon law) says about EMHC. It is not up to the person in the pew to determine if the priest is sufficiently incapacitated, or the crowd sufficiently large, to call on EMHC to assist in the orderly and reverent distribution of Holy Communion. The priest makes the determination – the bishop determines the guidelines for EMHC in his diocese.
"When the size of the congregation or the incapacity of the bishop, priest, or deacon requires it, the celebrant may be assisted by other bishops, priests, or deacons. If such ordinary ministers of Holy Communion are not present, “the priest may call upon extraordinary ministers to assist him, i.e., duly instituted acolytes or even other faithful who have been deputed for this purpose. In case of necessity, the priest may also depute suitable faithful for this single occasion (GIRM 162).”
Extraordinary Ministers of Holy Communion should receive sufficient spiritual, theological, and practical preparation to fulfill their role with knowledge and reverence. In all matters they should follow the guidance of the diocesan bishop ( Norms for the Distribution and Reception of Holy Communion Under Both Kinds for the Dioceses of the United States of America , NDRHC, no. 28). When recourse is had to Extraordinary Minister of Holy Communion, especially in the distribution of Holy Communion under both kinds, their number should not be increased beyond what is required for the orderly and reverent distribution of the Body and Blood of the Lord. In all matters such Extraordinary Ministers of Holy Communion should follow the guidance of the diocesan bishop (IBID)."